Safe to go back to the water

Dissolved organics in potable water can, under certain conditions, produce carcinogenic compounds. Hugh Lloyd, analytical product manager of ABB, examines how they are formed, and the technology available to detect them.

UNTREATED WATER can cause health problems. Water operators have a responsibility to produce safe, good-quality drinking water without discolouration, odour or an unpalatable taste.

The cause of many of the problems water companies face are dissolved organics. The real challenge is finding the causes of the dissolved organics. A key concern is the formation of trihalomethanes (THMs). These are potentially carcinogenic byproducts that can be formed when organic material in water reacts with chloramines. If the pH and temperature conditions are right, a reaction with the disinfectant used to make the water safer actually makes it more detrimental to health. The effects of THMs on health are far reaching, and they have possible links to heart, lung, kidney, liver, central-nervous- system damage, and bladder or colorectal cancer.

In the US, a study in California found a miscarriage rate of 15.7% for women who drank five or more glasses of cold water containing more than 75 parts per billion (ppb) of THM. This is compared with a miscarriage rate of 9.5% for women drinking water with low levels of THM.

Because of this, THM levels in public water supplies are limited to a maximum of 80ppb - and the controls are expected to get tighter.

The level of concern surrounding this issue can be seen from the situation in Nova Scotia in 2003. Due to the high level of dissolved organics in the waterways, there were 13 Nova Scotia municipalities that had THM levels above Canadian drinking-water quality guidelines. The concerns that high THM levels in drinking water may be linked to stillbirths or miscarriages led to a Department of Health warning to pregnant women.

Carbon filterHealth Canada suggested that the easiest way for women to reduce their exposure during pregnancy was to use a water pitcher with a carbon filter, a tap-mounted carbon filter, or bottled drinking water.

The challenge for water utilities is to accurately detect the variations of potential issues in the water passing through their plants. To protect people from the harmful effects of THMs, there must be highly accurate detection methods in place.

Previously, to detect THMs required costly and time-consuming laboratory tests. Recently, equipment, such as ABB's AV 400 series of water monitors has been introduced.

In order to provide a measure of the dissolved organics, these water monitors use calculations made by measuring a pulse of light at two wavelengths. One wavelength provides a reading from a turbidity photo detector and one from an UV photo detector.

These analysers can find dissolved organics quicker and more effectively than traditional methods, arguably removing the need for laboratory testing.

These improvements in detection devices are helping to reduce the likelihood of contamination by dissolved organics, leading to safer supplies of drinking water.

THMs are removed by passing the water through an activated carbon filter. This is an effective form of treatment when levels of THMs are known. Many factors affect THM levels - this means constant testing is necessary to monitor when filters need replacing.

Dissolved-organics monitors from ABB are being used by Yorkshire Water to prevent the formation of THMs. ABB's AV400 enables real-time monitoring of organic compounds.

Prior to the installation of the AV400s, water samples were regularly taken for laboratory analysis. But this presented a problem because it would take up to a week to get the results.

AV400 monitors measure the absorption of ultraviolet light, which is directly related to the level of organic matter in the water. Modelling the relationship between the level of organic matter and the subsequent formation of THMs has allowed Yorkshire Water's engineers to control them. This is by setting safe limits for organic material in the partially treated water heading for chlorination.

Jenny Banks, project engineer for research and development with Yorkshire Water, says: "Coagulation removes about 95% of organic matter before chlorination, but the ABB monitors allow us to fine-tune the treatment process."

Before the advent of UV254 technology, colour was the only contender for measuring organic matter in real time. The organic compounds commonly found in water abstracted from moorland, for example, typically give the raw water a characteristic yellow colour.

But, according to Banks, this approach was not accurate enough to apply to partially treated water. She says: "The level of colour is so low at that stage that the resolution is poor. UV254 provides a much more accurate indicator."

ABB's low-range AV400 monitors give a resolution of 0.01mg/l of dissolved organics over a range of 0-20mg/l.

Health concernThe measured value is updated every two seconds when the UV lamp is flashed and is calculated from more than 200 readings taken during the brief flash duration. This delivers better accuracy than conventional colour-testing technology.

Dissolved organics are a big problem for the water industry, and the presence of THMs in the public water supply is an important health concern. As the health risks continue to be identified, standards of drinking water are improving.

Technology is also progressing to enable water companies to take more safety measures and reduce the cost of these procedures. The new generation of water monitors will make testing easier, and reduce the risks of drinking water contaminated with dissolved organics.